Assessment of hindlimb locomotor strength in spinal cord transected rats through animal-robot contact force.

Robotic locomotor training devices have gained popularity in recent years, yet little has been reported regarding contact forces experienced by the subject performing automated locomotor training, particularly in animal models of neurological injury. The purpose of this study was to develop a means for acquiring contact forces between a robotic device and a rodent model of spinal cord injury through instrumentation of a robotic gait training device (the rat stepper) with miniature force/torque sensors. Sensors were placed at each interface between the robot arm and animal's hindlimb and underneath the stepping surface of both hindpaws (four sensors total). Twenty four female, Sprague-Dawley rats received mid-thoracic spinal cord transections as neonates and were included in the study. Of these 24 animals, training began for 18 animals at 21 days of age and continued for four weeks at five min/day, five days/week. The remaining six animals were untrained. Animal-robot contact forces were acquired for trained animals weekly and untrained animals every two weeks while stepping in the robotic device with both 60 and 90% of their body weight supported (BWS). Animals that received training significantly increased the number of weight supported steps over the four week training period. Analysis of raw contact forces revealed significant increases in forward swing and ground reaction forces during this time, and multiple aspects of animal-robot contact forces were significantly correlated with weight bearing stepping. However, when contact forces were normalized to animal body weight, these increasing trends were no longer present. Comparison of trained and untrained animals revealed significant differences in normalized ground reaction forces (both horizontal and vertical) and normalized forward swing force. Finally, both forward swing and ground reaction forces were significantly reduced at 90% BWS when compared to the 60% condition. These results suggest that measurement of animal-robot contact forces using the instrumented rat stepper can provide a sensitive and reliable measure of hindlimb locomotor strength and control of flexor and extensor muscle activity in neurologically impaired animals. Additionally, these measures may be useful as a means to quantify training intensity or dose-related functional outcomes of automated training.

Robot applied stance loading increases hindlimb muscle mass and stepping kinetics in a rat model of spinal cord injury.

Following spinal cord injury (SCI) reduced limb usage typically results in muscle atrophy. While robotic locomotor training has been shown to improve several aspects of stepping ability following SCI, little is known regarding the effects of automated training on the preservation of muscle function. The purpose of this study was to evaluate the effects of two robotic locomotor training algorithms on hindlimb strength and muscle mass in a rat model of SCI. Eighteen Sprague-Dawley rats received a mid-thoracic spinal cord transection at 5 days of age, and were randomly assigned to one of three groups: control (no training), standard robotic training, and robotic training with a downward force applied to the shank during the stance phase of gait. Training occurred 5 days/week for 5 min/day, and animals received 90% body weight support for all sessions. Following 4 weeks of training, vertical and propulsive ground reaction force during stepping and en vitro mass of two plantarflexor muscles were significantly increased for all of the trained animals when compared to the untrained control group. Post hoc analysis revealed that standard robotic training did not appear to increase ground reaction force and muscle mass to the same extent as the loaded condition. These results indicate that automated robotic training helps to preserve hindlimb muscle function in rats following SCI. Further, the addition of a plantarflexion stance load appears to promote greater increases in muscle mass and stepping kinetics.